blocks|key|1528367|text|我在过去使用过标准控件，只是为它添加了一个简单的ControlAdapter，它将覆盖默认行为，以便它可以在某些地方呈现s。即使你有不需要特殊行为的控件，这也很有效，因为额外的功能不会妨碍你。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1528368|请注意，这是一个特定的目的，并且是用.Net+2.0编写的，因此它可能不太适合您，但它至少应该给您一个起点。此外，您还必须在项目中使用.browserfile将其连接起来(请参阅本文末尾的示例)。|1528369|'This+codes+makes+the+dropdownlist+control+recognize+items+with+"--"
'for+the+label+or+items+with+an+OptionGroup+attribute+and+render+them
'as+<optgroup>+instead+of+<option>.
Public+Class+DropDownListAdapter
++++Inherits+System.Web.UI.WebControls.Adapters.WebControlAdapter

++++Protected+Overrides+Sub+RenderContents(ByVal+writer+As+HtmlTextWriter)
++++++++Dim+list+As+DropDownList+=+Me.Control
++++++++Dim+currentOptionGroup+As+String
++++++++Dim+renderedOptionGroups+As+New+Generic.List(Of+String)

++++++++For+Each+item+As+ListItem+In+list.Items
++++++++++++Page.ClientScript.RegisterForEventValidation(list.UniqueID,+item.Value)
++++++++++++If+item.Attributes("OptionGroup")+IsNot+Nothing+Then
++++++++++++++++'The+item+is+part+of+an+option+group
++++++++++++++++currentOptionGroup+=+item.Attributes("OptionGroup")
++++++++++++++++If+Not+renderedOptionGroups.Contains(currentOptionGroup)+Then
++++++++++++++++++++'the+header+was+not+written-+do+that+first
++++++++++++++++++++'TODO:+make+this+stack-based,+so+the+same+option+group+can+be+used+more+than+once+in+longer+select+element+(check+the+most-recent+stack+item+instead+of+anything+in+the+list)
++++++++++++++++++++If+(renderedOptionGroups.Count+>+0)+Then
++++++++++++++++++++++++RenderOptionGroupEndTag(writer)+'need+to+close+previous+group
++++++++++++++++++++End+If
++++++++++++++++++++RenderOptionGroupBeginTag(currentOptionGroup,+writer)
++++++++++++++++++++renderedOptionGroups.Add(currentOptionGroup)
++++++++++++++++End+If
++++++++++++++++RenderListItem(item,+writer)
++++++++++++ElseIf+item.Text+=+"--"+Then+'simple+separator
++++++++++++++++RenderOptionGroupBeginTag("--",+writer)
++++++++++++++++RenderOptionGroupEndTag(writer)
++++++++++++Else
++++++++++++++++'default+behavior:+render+the+list+item+as+normal
++++++++++++++++RenderListItem(item,+writer)
++++++++++++End+If
++++++++Next+item

++++++++If+renderedOptionGroups.Count+>+0+Then
++++++++++++RenderOptionGroupEndTag(writer)
++++++++End+If
++++End+Sub

++++Private+Sub+RenderOptionGroupBeginTag(ByVal+name+As+String,+ByVal+writer+As+HtmlTextWriter)
++++++++writer.WriteBeginTag("optgroup")
++++++++writer.WriteAttribute("label",+name)
++++++++writer.Write(HtmlTextWriter.TagRightChar)
++++++++writer.WriteLine()
++++End+Sub

++++Private+Sub+RenderOptionGroupEndTag(ByVal+writer+As+HtmlTextWriter)
++++++++writer.WriteEndTag("optgroup")
++++++++writer.WriteLine()
++++End+Sub

++++Private+Sub+RenderListItem(ByVal+item+As+ListItem,+ByVal+writer+As+HtmlTextWriter)
++++++++writer.WriteBeginTag("option")
++++++++writer.WriteAttribute("value",+item.Value,+True)
++++++++If+item.Selected+Then
++++++++++++writer.WriteAttribute("selected",+"selected",+False)
++++++++End+If

++++++++For+Each+key+As+String+In+item.Attributes.Keys
++++++++++++writer.WriteAttribute(key,+item.Attributes(key))
++++++++Next+key

++++++++writer.Write(HtmlTextWriter.TagRightChar)
++++++++HttpUtility.HtmlEncode(item.Text,+writer)
++++++++writer.WriteEndTag("option")
++++++++writer.WriteLine()
++++End+Sub
End+Class|code-block|syntax|javascript|1528370|下面是同一个类的C#实现：|1528371|/*+This+codes+makes+the+dropdownlist+control+recognize+items+with+"--"
+*+for+the+label+or+items+with+an+OptionGroup+attribute+and+render+them
+*+as+<optgroup>+instead+of+<option>.
+*/
public+class+DropDownListAdapter+:+WebControlAdapter
{
++++protected+override+void+RenderContents(HtmlTextWriter+writer)
++++{
++++++++//System.Web.HttpContext.Current.Response.Write("here");
++++++++var+list+=+(DropDownList)this.Control;
++++++++string+currentOptionGroup;
++++++++var+renderedOptionGroups+=+new+List<string>();

++++++++foreach+(ListItem+item+in+list.Items)
++++++++{
++++++++++++Page.ClientScript.RegisterForEventValidation(list.UniqueID,+item.Value);
++++++++++++//Is+the+item+part+of+an+option+group?
++++++++++++if+(item.Attributes["OptionGroup"]+!=+null)
++++++++++++{
++++++++++++++++currentOptionGroup+=+item.Attributes["OptionGroup"];
++++++++++++++++//Was+the+option+header+already+written,+then+just+render+the+list+item
++++++++++++++++if+(renderedOptionGroups.Contains(currentOptionGroup))
++++++++++++++++++++RenderListItem(item,+writer);
++++++++++++++++//The+header+was+not+written,do+that+first
++++++++++++++++else
++++++++++++++++{
++++++++++++++++++++//Close+previous+group
++++++++++++++++++++if+(renderedOptionGroups.Count+>+0)
++++++++++++++++++++++++RenderOptionGroupEndTag(writer);

++++++++++++++++++++RenderOptionGroupBeginTag(currentOptionGroup,+writer);
++++++++++++++++++++renderedOptionGroups.Add(currentOptionGroup);
++++++++++++++++++++RenderListItem(item,+writer);
++++++++++++++++}
++++++++++++}
++++++++++++//Simple+separator
++++++++++++else+if+(item.Text+==+"--")
++++++++++++{
++++++++++++++++RenderOptionGroupBeginTag("--",+writer);
++++++++++++++++RenderOptionGroupEndTag(writer);
++++++++++++}
++++++++++++//Default+behavior,+render+the+list+item+as+normal
++++++++++++else
++++++++++++++++RenderListItem(item,+writer);
++++++++}

++++++++if+(renderedOptionGroups.Count+>+0)
++++++++++++RenderOptionGroupEndTag(writer);
++++}

++++private+void+RenderOptionGroupBeginTag(string+name,+HtmlTextWriter+writer)
++++{
++++++++writer.WriteBeginTag("optgroup");
++++++++writer.WriteAttribute("label",+name);
++++++++writer.Write(HtmlTextWriter.TagRightChar);
++++++++writer.WriteLine();
++++}
++++private+void+RenderOptionGroupEndTag(HtmlTextWriter+writer)
++++{
++++++++writer.WriteEndTag("optgroup");
++++++++writer.WriteLine();
++++}
++++private+void+RenderListItem(ListItem+item,+HtmlTextWriter+writer)
++++{
++++++++writer.WriteBeginTag("option");
++++++++writer.WriteAttribute("value",+item.Value,+true);
++++++++if+(item.Selected)
++++++++++++writer.WriteAttribute("selected",+"selected",+false);

++++++++foreach+(string+key+in+item.Attributes.Keys)
++++++++++++writer.WriteAttribute(key,+item.Attributes[key]);

++++++++writer.Write(HtmlTextWriter.TagRightChar);
++++++++HttpUtility.HtmlEncode(item.Text,+writer);
++++++++writer.WriteEndTag("option");
++++++++writer.WriteLine();
++++}
}|1528372|我的浏览器文件名为"App_Browsers\BrowserFile.browser“，如下所示：|1528373|
<browsers>
+++<browser+refID="Default">
++++++<controlAdapters>
++++++++<adapter+controlType="System.Web.UI.WebControls.DropDownList"+
+++++++++++++++adapterType="DropDownListAdapter"+/>
++++++</controlAdapters>
+++</browser>
</browsers>|1528374|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.web.ui.adapters.controladapter.aspx^0|O|E|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|15|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|17|8|@]|9|@]|C|$I|J]]|$1|O|3|P|5|6|7|18|8|@]|9|@]|C|$]]|$1|Q|3|R|5|H|7|19|8|@]|9|@]|C|$I|J]]|$1|S|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

I've used the standard control in the past, and just added a simple <a href="http://msdn.microsoft.com/en-us/library/system.web.ui.adapters.controladapter.aspx" rel="nofollow noreferrer">ControlAdapter</a> for it that would override the default behavior so it could render &lt;optgroup>s in certain places. This works great even if you have controls that don't need the special behavior, because the additional feature doesn't get in the way.

Note that this was for a specific purpose and written in .Net 2.0, so it may not suit you as well, but it should at least give you a starting point. Also, you have to hook it up using a .browserfile in your project (see the end of the post for an example).

<pre class="lang-vb prettyprint-override"><code>'This codes makes the dropdownlist control recognize items with "--"
'for the label or items with an OptionGroup attribute and render them
'as &lt;optgroup&gt; instead of &lt;option&gt;.
Public Class DropDownListAdapter
 Inherits System.Web.UI.WebControls.Adapters.WebControlAdapter

 Protected Overrides Sub RenderContents(ByVal writer As HtmlTextWriter)
 Dim list As DropDownList = Me.Control
 Dim currentOptionGroup As String
 Dim renderedOptionGroups As New Generic.List(Of String)

 For Each item As ListItem In list.Items
 Page.ClientScript.RegisterForEventValidation(list.UniqueID, item.Value)
 If item.Attributes("OptionGroup") IsNot Nothing Then
 'The item is part of an option group
 currentOptionGroup = item.Attributes("OptionGroup")
 If Not renderedOptionGroups.Contains(currentOptionGroup) Then
 'the header was not written- do that first
 'TODO: make this stack-based, so the same option group can be used more than once in longer select element (check the most-recent stack item instead of anything in the list)
 If (renderedOptionGroups.Count &gt; 0) Then
 RenderOptionGroupEndTag(writer) 'need to close previous group
 End If
 RenderOptionGroupBeginTag(currentOptionGroup, writer)
 renderedOptionGroups.Add(currentOptionGroup)
 End If
 RenderListItem(item, writer)
 ElseIf item.Text = "--" Then 'simple separator
 RenderOptionGroupBeginTag("--", writer)
 RenderOptionGroupEndTag(writer)
 Else
 'default behavior: render the list item as normal
 RenderListItem(item, writer)
 End If
 Next item

 If renderedOptionGroups.Count &gt; 0 Then
 RenderOptionGroupEndTag(writer)
 End If
 End Sub

 Private Sub RenderOptionGroupBeginTag(ByVal name As String, ByVal writer As HtmlTextWriter)
 writer.WriteBeginTag("optgroup")
 writer.WriteAttribute("label", name)
 writer.Write(HtmlTextWriter.TagRightChar)
 writer.WriteLine()
 End Sub

 Private Sub RenderOptionGroupEndTag(ByVal writer As HtmlTextWriter)
 writer.WriteEndTag("optgroup")
 writer.WriteLine()
 End Sub

 Private Sub RenderListItem(ByVal item As ListItem, ByVal writer As HtmlTextWriter)
 writer.WriteBeginTag("option")
 writer.WriteAttribute("value", item.Value, True)
 If item.Selected Then
 writer.WriteAttribute("selected", "selected", False)
 End If

 For Each key As String In item.Attributes.Keys
 writer.WriteAttribute(key, item.Attributes(key))
 Next key

 writer.Write(HtmlTextWriter.TagRightChar)
 HttpUtility.HtmlEncode(item.Text, writer)
 writer.WriteEndTag("option")
 writer.WriteLine()
 End Sub
End Class
</code></pre>

Here's a C# implementation of the same Class:

<pre><code>/* This codes makes the dropdownlist control recognize items with "--"
 * for the label or items with an OptionGroup attribute and render them
 * as &lt;optgroup&gt; instead of &lt;option&gt;.
 */
public class DropDownListAdapter : WebControlAdapter
{
 protected override void RenderContents(HtmlTextWriter writer)
 {
 //System.Web.HttpContext.Current.Response.Write("here");
 var list = (DropDownList)this.Control;
 string currentOptionGroup;
 var renderedOptionGroups = new List&lt;string&gt;();

 foreach (ListItem item in list.Items)
 {
 Page.ClientScript.RegisterForEventValidation(list.UniqueID, item.Value);
 //Is the item part of an option group?
 if (item.Attributes["OptionGroup"] != null)
 {
 currentOptionGroup = item.Attributes["OptionGroup"];
 //Was the option header already written, then just render the list item
 if (renderedOptionGroups.Contains(currentOptionGroup))
 RenderListItem(item, writer);
 //The header was not written,do that first
 else
 {
 //Close previous group
 if (renderedOptionGroups.Count &gt; 0)
 RenderOptionGroupEndTag(writer);

 RenderOptionGroupBeginTag(currentOptionGroup, writer);
 renderedOptionGroups.Add(currentOptionGroup);
 RenderListItem(item, writer);
 }
 }
 //Simple separator
 else if (item.Text == "--")
 {
 RenderOptionGroupBeginTag("--", writer);
 RenderOptionGroupEndTag(writer);
 }
 //Default behavior, render the list item as normal
 else
 RenderListItem(item, writer);
 }

 if (renderedOptionGroups.Count &gt; 0)
 RenderOptionGroupEndTag(writer);
 }

 private void RenderOptionGroupBeginTag(string name, HtmlTextWriter writer)
 {
 writer.WriteBeginTag("optgroup");
 writer.WriteAttribute("label", name);
 writer.Write(HtmlTextWriter.TagRightChar);
 writer.WriteLine();
 }
 private void RenderOptionGroupEndTag(HtmlTextWriter writer)
 {
 writer.WriteEndTag("optgroup");
 writer.WriteLine();
 }
 private void RenderListItem(ListItem item, HtmlTextWriter writer)
 {
 writer.WriteBeginTag("option");
 writer.WriteAttribute("value", item.Value, true);
 if (item.Selected)
 writer.WriteAttribute("selected", "selected", false);

 foreach (string key in item.Attributes.Keys)
 writer.WriteAttribute(key, item.Attributes[key]);

 writer.Write(HtmlTextWriter.TagRightChar);
 HttpUtility.HtmlEncode(item.Text, writer);
 writer.WriteEndTag("option");
 writer.WriteLine();
 }
}
</code></pre>

My browser file was named "App_Browsers\BrowserFile.browser" and looked like this:

<pre><code>&lt;!--
 You can find existing browser definitions at
 &lt;windir&gt;\Microsoft.NET\Framework\&lt;ver&gt;\CONFIG\Browsers
--&gt;
&lt;browsers&gt;
 &lt;browser refID="Default"&gt;
 &lt;controlAdapters&gt;
 &lt;adapter controlType="System.Web.UI.WebControls.DropDownList" 
 adapterType="DropDownListAdapter" /&gt;
 &lt;/controlAdapters&gt;
 &lt;/browser&gt;
&lt;/browsers&gt;
</code></pre>

blocks|key|1743389|text|Sharp+Pieces+project+on+CodePlex解决了这个(和其他几个)控制限制。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1743390|entityMap|0|LINK|mutability|MUTABLE|url|http://www.codeplex.com/SharpPieces^0|0|W|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

The <a href="http://www.codeplex.com/SharpPieces" rel="nofollow noreferrer">Sharp Pieces project on CodePlex</a> solves this (and several other) control limitations.

blocks|key|1743419|text|谢谢，Joel！各位..。如果你想要，这里是C#版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743420|using+System;
using+System.Web.UI.WebControls.Adapters;
using+System.Web.UI;
using+System.Web.UI.WebControls;
using+System.Collections.Generic;
using+System.Web;

//This+codes+makes+the+dropdownlist+control+recognize+items+with+"--"'
//for+the+label+or+items+with+an+OptionGroup+attribute+and+render+them'
//as++instead+of+.'
public+class+DropDownListAdapter+:+WebControlAdapter
{

++++protected+override+void+RenderContents(HtmlTextWriter+writer)
++++{
++++++++DropDownList+list+=+Control+as+DropDownList;
++++++++string+currentOptionGroup;
++++++++List+renderedOptionGroups+=+new+List();

++++++++foreach(ListItem+item+in+list.Items)
++++++++{
++++++++++++if+(item.Attributes["OptionGroup"]+!=+null)
++++++++++++{
++++++++++++++++//'The+item+is+part+of+an+option+group'
++++++++++++++++currentOptionGroup+=+item.Attributes["OptionGroup"];
++++++++++++++++//'the+option+header+was+already+written,+just+render+the+list+item'
++++++++++++++++if(renderedOptionGroups.Contains(currentOptionGroup))
++++++++++++++++++++RenderListItem(item,+writer);
++++++++++++++++else
++++++++++++++++{
++++++++++++++++++++//the+header+was+not+written-+do+that+first'
++++++++++++++++++++if+(renderedOptionGroups.Count+>+0)
++++++++++++++++++++++++RenderOptionGroupEndTag(writer);+//'need+to+close+previous+group'
++++++++++++++++++++RenderOptionGroupBeginTag(currentOptionGroup,+writer);
++++++++++++++++++++renderedOptionGroups.Add(currentOptionGroup);
++++++++++++++++++++RenderListItem(item,+writer);
++++++++++++++++}
++++++++++++}
++++++++++++else+if+(item.Text+==+"--")+//simple+separator
++++++++++++{
++++++++++++++++RenderOptionGroupBeginTag("--",+writer);
++++++++++++++++RenderOptionGroupEndTag(writer);
++++++++++++}
++++++++++++else
++++++++++++{
++++++++++++++++//default+behavior:+render+the+list+item+as+normal'
++++++++++++++++RenderListItem(item,+writer);
++++++++++++}
++++++++}

++++++++if(renderedOptionGroups.Count+>+0)
++++++++++++RenderOptionGroupEndTag(writer);
++++}

++++private+void+RenderOptionGroupBeginTag(string+name,+HtmlTextWriter+writer)
++++{
++++++++writer.WriteBeginTag("optgroup");
++++++++writer.WriteAttribute("label",+name);
++++++++writer.Write(HtmlTextWriter.TagRightChar);
++++++++writer.WriteLine();
++++}

++++private+void+RenderOptionGroupEndTag(HtmlTextWriter+writer)
++++{
++++++++writer.WriteEndTag("optgroup");
++++++++writer.WriteLine();
++++}

++++private+void+RenderListItem(ListItem+item,+HtmlTextWriter+writer)
++++{
++++++++writer.WriteBeginTag("option");
++++++++writer.WriteAttribute("value",+item.Value,+true);
++++++++if+(item.Selected)
++++++++++++writer.WriteAttribute("selected",+"selected",+false);


++++++++foreach+(string+key+in+item.Attributes.Keys)
++++++++++++writer.WriteAttribute(key,+item.Attributes[key]);

++++++++writer.Write(HtmlTextWriter.TagRightChar);
++++++++HttpUtility.HtmlEncode(item.Text,+writer);
++++++++writer.WriteEndTag("option");
++++++++writer.WriteLine();
++++}

}|code-block|syntax|javascript|1743421|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Thanks Joel! everyone... here's C# version if you want it:

<pre><code>

using System;
using System.Web.UI.WebControls.Adapters;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Collections.Generic;
using System.Web;

//This codes makes the dropdownlist control recognize items with "--"'
//for the label or items with an OptionGroup attribute and render them'
//as instead of .'
public class DropDownListAdapter : WebControlAdapter
{

 protected override void RenderContents(HtmlTextWriter writer)
 {
 DropDownList list = Control as DropDownList;
 string currentOptionGroup;
 List renderedOptionGroups = new List();

 foreach(ListItem item in list.Items)
 {
 if (item.Attributes["OptionGroup"] != null)
 {
 //'The item is part of an option group'
 currentOptionGroup = item.Attributes["OptionGroup"];
 //'the option header was already written, just render the list item'
 if(renderedOptionGroups.Contains(currentOptionGroup))
 RenderListItem(item, writer);
 else
 {
 //the header was not written- do that first'
 if (renderedOptionGroups.Count > 0)
 RenderOptionGroupEndTag(writer); //'need to close previous group'
 RenderOptionGroupBeginTag(currentOptionGroup, writer);
 renderedOptionGroups.Add(currentOptionGroup);
 RenderListItem(item, writer);
 }
 }
 else if (item.Text == "--") //simple separator
 {
 RenderOptionGroupBeginTag("--", writer);
 RenderOptionGroupEndTag(writer);
 }
 else
 {
 //default behavior: render the list item as normal'
 RenderListItem(item, writer);
 }
 }

 if(renderedOptionGroups.Count > 0)
 RenderOptionGroupEndTag(writer);
 }

 private void RenderOptionGroupBeginTag(string name, HtmlTextWriter writer)
 {
 writer.WriteBeginTag("optgroup");
 writer.WriteAttribute("label", name);
 writer.Write(HtmlTextWriter.TagRightChar);
 writer.WriteLine();
 }

 private void RenderOptionGroupEndTag(HtmlTextWriter writer)
 {
 writer.WriteEndTag("optgroup");
 writer.WriteLine();
 }

 private void RenderListItem(ListItem item, HtmlTextWriter writer)
 {
 writer.WriteBeginTag("option");
 writer.WriteAttribute("value", item.Value, true);
 if (item.Selected)
 writer.WriteAttribute("selected", "selected", false);


 foreach (string key in item.Attributes.Keys)
 writer.WriteAttribute(key, item.Attributes[key]);

 writer.Write(HtmlTextWriter.TagRightChar);
 HttpUtility.HtmlEncode(item.Text, writer);
 writer.WriteEndTag("option");
 writer.WriteLine();
 }

}



</code></pre>

blocks|key|1743466|text|我使用反射器来了解不支持的原因。这就是为什么。在ListControl的render方法中，没有创建optgroup的条件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743467|protected+internal+override+void+RenderContents(HtmlTextWriter+writer)
++++{
++++++++ListItemCollection+items+=+this.Items;
++++++++int+count+=+items.Count;
++++++++if+(count+>+0)
++++++++{
++++++++++++bool+flag+=+false;
++++++++++++for+(int+i+=+0;+i+<+count;+i%2B%2B)
++++++++++++{
++++++++++++++++ListItem+item+=+items[i];
++++++++++++++++if+(item.Enabled)
++++++++++++++++{
++++++++++++++++++++writer.WriteBeginTag("option");
++++++++++++++++++++if+(item.Selected)
++++++++++++++++++++{
++++++++++++++++++++++++if+(flag)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++this.VerifyMultiSelect();
++++++++++++++++++++++++}
++++++++++++++++++++++++flag+=+true;
++++++++++++++++++++++++writer.WriteAttribute("selected",+"selected");
++++++++++++++++++++}
++++++++++++++++++++writer.WriteAttribute("value",+item.Value,+true);
++++++++++++++++++++if+(item.HasAttributes)
++++++++++++++++++++{
++++++++++++++++++++++++item.Attributes.Render(writer);
++++++++++++++++++++}
++++++++++++++++++++if+(this.Page+!=+null)
++++++++++++++++++++{
++++++++++++++++++++++++this.Page.ClientScript.RegisterForEventValidation(this.UniqueID,+item.Value);
++++++++++++++++++++}
++++++++++++++++++++writer.Write('>');
++++++++++++++++++++HttpUtility.HtmlEncode(item.Text,+writer);
++++++++++++++++++++writer.WriteEndTag("option");
++++++++++++++++++++writer.WriteLine();
++++++++++++++++}
++++++++++++}
++++++++}
++++}|code-block|syntax|javascript|1743468|因此，我创建了自己的dropdown控件，并覆盖了RenderContents方法。这就是我的控制。工作得很好。我使用与微软完全相同的代码，只是增加了一点条件来支持listItem具有属性optgroup来创建一个optgroup，而不是一个选项。|1743469|给我一些反馈|1743470|public+class+DropDownListWithOptionGroup+:+DropDownList
++{
++++public+const+string+OptionGroupTag+=+"optgroup";
++++private+const+string+OptionTag+=+"option";
++++protected+override+void+RenderContents(System.Web.UI.HtmlTextWriter+writer)
++++{
++++++ListItemCollection+items+=+this.Items;
++++++int+count+=+items.Count;+++++
++++++string+tag;
++++++string+optgroupLabel;
++++++if+(count+>+0)
++++++{
++++++++bool+flag+=+false;
++++++++for+(int+i+=+0;+i+<+count;+i%2B%2B)
++++++++{
++++++++++tag+=+OptionTag;
++++++++++optgroupLabel+=+null;
++++++++++ListItem+item+=+items[i];
++++++++++if+(item.Enabled)
++++++++++{
++++++++++++if+(item.Attributes+!=+null+&&+item.Attributes.Count+>+0+&&+item.Attributes[OptionGroupTag]+!=+null)
++++++++++++{
++++++++++++++tag+=+OptionGroupTag;
++++++++++++++optgroupLabel+=+item.Attributes[OptionGroupTag];
++++++++++++}+++++++++++
++++++++++++writer.WriteBeginTag(tag);
++++++++++++//+NOTE(cboivin):+Is+optionGroup
++++++++++++if+(!string.IsNullOrEmpty(optgroupLabel))
++++++++++++{
++++++++++++++writer.WriteAttribute("label",+optgroupLabel);
++++++++++++}
++++++++++++else
++++++++++++{
++++++++++++++if+(item.Selected)
++++++++++++++{
++++++++++++++++if+(flag)
++++++++++++++++{
++++++++++++++++++this.VerifyMultiSelect();
++++++++++++++++}
++++++++++++++++flag+=+true;
++++++++++++++++writer.WriteAttribute("selected",+"selected");
++++++++++++++}
++++++++++++++writer.WriteAttribute("value",+item.Value,+true);
++++++++++++++if+(item.Attributes+!=+null+&&+item.Attributes.Count+>+0)
++++++++++++++{
++++++++++++++++item.Attributes.Render(writer);
++++++++++++++}
++++++++++++++if+(this.Page+!=+null)
++++++++++++++{
++++++++++++++++this.Page.ClientScript.RegisterForEventValidation(this.UniqueID,+item.Value);
++++++++++++++}
++++++++++++}
++++++++++++writer.Write('>');
++++++++++++HttpUtility.HtmlEncode(item.Text,+writer);
++++++++++++writer.WriteEndTag(tag);
++++++++++++writer.WriteLine();
++++++++++}
++++++++}
++++++}

++++}
++}|1743471|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I use the reflector to see why is not supported. There is why. In the render method of the ListControl no condition is there to create the optgroup. 

<pre><code>protected internal override void RenderContents(HtmlTextWriter writer)
 {
 ListItemCollection items = this.Items;
 int count = items.Count;
 if (count &gt; 0)
 {
 bool flag = false;
 for (int i = 0; i &lt; count; i++)
 {
 ListItem item = items[i];
 if (item.Enabled)
 {
 writer.WriteBeginTag("option");
 if (item.Selected)
 {
 if (flag)
 {
 this.VerifyMultiSelect();
 }
 flag = true;
 writer.WriteAttribute("selected", "selected");
 }
 writer.WriteAttribute("value", item.Value, true);
 if (item.HasAttributes)
 {
 item.Attributes.Render(writer);
 }
 if (this.Page != null)
 {
 this.Page.ClientScript.RegisterForEventValidation(this.UniqueID, item.Value);
 }
 writer.Write('&gt;');
 HttpUtility.HtmlEncode(item.Text, writer);
 writer.WriteEndTag("option");
 writer.WriteLine();
 }
 }
 }
 }
</code></pre>

So i create my own dropdown Control with an override of the method RenderContents. There is my control. Is working fine. I use exactly the same code of Microsoft, just add a little condition to support listItem having attribute optgroup to create an optgroup and not a option.

Give me some feed back

<pre><code>public class DropDownListWithOptionGroup : DropDownList
 {
 public const string OptionGroupTag = "optgroup";
 private const string OptionTag = "option";
 protected override void RenderContents(System.Web.UI.HtmlTextWriter writer)
 {
 ListItemCollection items = this.Items;
 int count = items.Count; 
 string tag;
 string optgroupLabel;
 if (count &gt; 0)
 {
 bool flag = false;
 for (int i = 0; i &lt; count; i++)
 {
 tag = OptionTag;
 optgroupLabel = null;
 ListItem item = items[i];
 if (item.Enabled)
 {
 if (item.Attributes != null &amp;&amp; item.Attributes.Count &gt; 0 &amp;&amp; item.Attributes[OptionGroupTag] != null)
 {
 tag = OptionGroupTag;
 optgroupLabel = item.Attributes[OptionGroupTag];
 } 
 writer.WriteBeginTag(tag);
 // NOTE(cboivin): Is optionGroup
 if (!string.IsNullOrEmpty(optgroupLabel))
 {
 writer.WriteAttribute("label", optgroupLabel);
 }
 else
 {
 if (item.Selected)
 {
 if (flag)
 {
 this.VerifyMultiSelect();
 }
 flag = true;
 writer.WriteAttribute("selected", "selected");
 }
 writer.WriteAttribute("value", item.Value, true);
 if (item.Attributes != null &amp;&amp; item.Attributes.Count &gt; 0)
 {
 item.Attributes.Render(writer);
 }
 if (this.Page != null)
 {
 this.Page.ClientScript.RegisterForEventValidation(this.UniqueID, item.Value);
 }
 }
 writer.Write('&gt;');
 HttpUtility.HtmlEncode(item.Text, writer);
 writer.WriteEndTag(tag);
 writer.WriteLine();
 }
 }
 }

 }
 }
</code></pre>

blocks|key|1743501|text|正如上面的答案所示，重载RenderContents方法确实有效。您还必须记住更改视图状态。在UpdatePanels中使用未更改的视图状态时，我遇到了一个问题。这是从Sharp+Pieces+Project中提取的部分。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1743502|+Protected+Overloads+Overrides+Sub+RenderContents(ByVal+writer+As+HtmlTextWriter)
++++Dim+list+As+DropDownList+=+Me

++++Dim+currentOptionGroup+As+String
++++Dim+renderedOptionGroups+As+New+List(Of+String)()

++++For+Each+item+As+ListItem+In+list.Items
++++++++If+item.Attributes("OptionGroup")+Is+Nothing+Then
++++++++++++RenderListItem(item,+writer)
++++++++Else
++++++++++++currentOptionGroup+=+item.Attributes("OptionGroup")

++++++++++++If+renderedOptionGroups.Contains(currentOptionGroup)+Then
++++++++++++++++RenderListItem(item,+writer)
++++++++++++Else
++++++++++++++++If+renderedOptionGroups.Count+>+0+Then
++++++++++++++++++++RenderOptionGroupEndTag(writer)
++++++++++++++++End+If

++++++++++++++++RenderOptionGroupBeginTag(currentOptionGroup,+writer)
++++++++++++++++renderedOptionGroups.Add(currentOptionGroup)

++++++++++++++++RenderListItem(item,+writer)
++++++++++++End+If
++++++++End+If
++++Next

++++If+renderedOptionGroups.Count+>+0+Then
++++++++RenderOptionGroupEndTag(writer)
++++End+If
End+Sub

Private+Sub+RenderOptionGroupBeginTag(ByVal+name+As+String,+ByVal+writer+As+HtmlTextWriter)
++++writer.WriteBeginTag("optgroup")
++++writer.WriteAttribute("label",+name)
++++writer.Write(HtmlTextWriter.TagRightChar)
++++writer.WriteLine()
End+Sub

Private+Sub+RenderOptionGroupEndTag(ByVal+writer+As+HtmlTextWriter)
++++writer.WriteEndTag("optgroup")
++++writer.WriteLine()
End+Sub

Private+Sub+RenderListItem(ByVal+item+As+ListItem,+ByVal+writer+As+HtmlTextWriter)
++++writer.WriteBeginTag("option")
++++writer.WriteAttribute("value",+item.Value,+True)

++++If+item.Selected+Then
++++++++writer.WriteAttribute("selected",+"selected",+False)
++++End+If

++++For+Each+key+As+String+In+item.Attributes.Keys
++++++++writer.WriteAttribute(key,+item.Attributes(key))
++++Next

++++writer.Write(HtmlTextWriter.TagRightChar)
++++HttpUtility.HtmlEncode(item.Text,+writer)
++++writer.WriteEndTag("option")
++++writer.WriteLine()
End+Sub
Protected+Overrides+Function+SaveViewState()+As+Object
++++'+Create+an+object+array+with+one+element+for+the+CheckBoxList's
++++'+ViewState+contents,+and+one+element+for+each+ListItem+in+skmCheckBoxList
++++Dim+state(Me.Items.Count+%2B+1+-+1)+As+Object+'stupid+vb+array
++++Dim+baseState+As+Object+=+MyBase.SaveViewState()

++++state(0)+=+baseState
++++'+Now,+see+if+we+even+need+to+save+the+view+state
++++Dim+itemHasAttributes+As+Boolean+=+False

++++For+i+As+Integer+=+0+To+Me.Items.Count+-+1
++++++++If+Me.Items(i).Attributes.Count+>+0+Then
++++++++++++itemHasAttributes+=+True
++++++++++++'+Create+an+array+of+the+item's+Attribute's+keys+and+values
++++++++++++Dim+attribKV(Me.Items(i).Attributes.Count+*+2+-+1)+As+Object+'stupid+vb+array
++++++++++++Dim+k+As+Integer+=+0
++++++++++++For+Each+key+As+String+In+Me.Items(i).Attributes.Keys
++++++++++++++++attribKV(k)+=+key
++++++++++++++++k+%2B=+1
++++++++++++++++attribKV(k)+=+Me.Items(i).Attributes(key)
++++++++++++++++k+%2B=+1
++++++++++++Next
++++++++++++state(i+%2B+1)+=+attribKV
++++++++End+If
++++Next
++++'+return+either+baseState+or+state,+depending+on+whether+or+not
++++'+any+ListItems+had+attributes
++++If+(itemHasAttributes)+Then
++++++++Return+state
++++Else
++++++++Return+baseState
++++End+If
End+Function


Protected+Overrides+Sub+LoadViewState(ByVal+savedState+As+Object)
++++If+savedState+Is+Nothing+Then+Return
++++'+see+if+savedState+is+an+object+or+object+array
++++If+Not+savedState.GetType.GetElementType()+Is+Nothing+AndAlso+savedState.GetType.GetElementType().Equals(GetType(Object))+Then

++++++++'+we+have+just+the+base+state
++++++++MyBase.LoadViewState(savedState(0))
++++++++'we+have+an+array+of+items+with+attributes
++++++++Dim+state()+As+Object+=+savedState
++++++++MyBase.LoadViewState(state(0))+++'/+load+the+base+state
++++++++For+i+As+Integer+=+1+To+state.Length+-+1
++++++++++++If+Not+state(i)+Is+Nothing+Then
++++++++++++++++'+Load+back+in+the+attributes
++++++++++++++++Dim+attribKV()+As+Object+=+state(i)
++++++++++++++++For+k+As+Integer+=+0+To+attribKV.Length+-+1+Step+%2B2
++++++++++++++++++++Me.Items(i+-+1).Attributes.Add(attribKV(k).ToString(),+attribKV(k+%2B+1).ToString())
++++++++++++++++Next
++++++++++++End+If
++++++++Next
++++Else
++++++++'load+it+normal
++++++++MyBase.LoadViewState(savedState)
++++End+If
End+Sub|code-block|syntax|javascript|1743503|entityMap|0|LINK|mutability|MUTABLE|url|http://www.codeplex.com/SharpPieces^0|2C|K|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

As the answers above that overload the RenderContents method do work. You also have to remember to alter the viewstate. I have come into an issue when using the non-altered viewstate in UpdatePanels. This has parts taken from the <a href="http://www.codeplex.com/SharpPieces" rel="nofollow noreferrer">Sharp Pieces Project</a>.

<pre class="lang-vb prettyprint-override"><code> Protected Overloads Overrides Sub RenderContents(ByVal writer As HtmlTextWriter)
 Dim list As DropDownList = Me

 Dim currentOptionGroup As String
 Dim renderedOptionGroups As New List(Of String)()

 For Each item As ListItem In list.Items
 If item.Attributes("OptionGroup") Is Nothing Then
 RenderListItem(item, writer)
 Else
 currentOptionGroup = item.Attributes("OptionGroup")

 If renderedOptionGroups.Contains(currentOptionGroup) Then
 RenderListItem(item, writer)
 Else
 If renderedOptionGroups.Count &gt; 0 Then
 RenderOptionGroupEndTag(writer)
 End If

 RenderOptionGroupBeginTag(currentOptionGroup, writer)
 renderedOptionGroups.Add(currentOptionGroup)

 RenderListItem(item, writer)
 End If
 End If
 Next

 If renderedOptionGroups.Count &gt; 0 Then
 RenderOptionGroupEndTag(writer)
 End If
End Sub

Private Sub RenderOptionGroupBeginTag(ByVal name As String, ByVal writer As HtmlTextWriter)
 writer.WriteBeginTag("optgroup")
 writer.WriteAttribute("label", name)
 writer.Write(HtmlTextWriter.TagRightChar)
 writer.WriteLine()
End Sub

Private Sub RenderOptionGroupEndTag(ByVal writer As HtmlTextWriter)
 writer.WriteEndTag("optgroup")
 writer.WriteLine()
End Sub

Private Sub RenderListItem(ByVal item As ListItem, ByVal writer As HtmlTextWriter)
 writer.WriteBeginTag("option")
 writer.WriteAttribute("value", item.Value, True)

 If item.Selected Then
 writer.WriteAttribute("selected", "selected", False)
 End If

 For Each key As String In item.Attributes.Keys
 writer.WriteAttribute(key, item.Attributes(key))
 Next

 writer.Write(HtmlTextWriter.TagRightChar)
 HttpUtility.HtmlEncode(item.Text, writer)
 writer.WriteEndTag("option")
 writer.WriteLine()
End Sub
Protected Overrides Function SaveViewState() As Object
 ' Create an object array with one element for the CheckBoxList's
 ' ViewState contents, and one element for each ListItem in skmCheckBoxList
 Dim state(Me.Items.Count + 1 - 1) As Object 'stupid vb array
 Dim baseState As Object = MyBase.SaveViewState()

 state(0) = baseState
 ' Now, see if we even need to save the view state
 Dim itemHasAttributes As Boolean = False

 For i As Integer = 0 To Me.Items.Count - 1
 If Me.Items(i).Attributes.Count &gt; 0 Then
 itemHasAttributes = True
 ' Create an array of the item's Attribute's keys and values
 Dim attribKV(Me.Items(i).Attributes.Count * 2 - 1) As Object 'stupid vb array
 Dim k As Integer = 0
 For Each key As String In Me.Items(i).Attributes.Keys
 attribKV(k) = key
 k += 1
 attribKV(k) = Me.Items(i).Attributes(key)
 k += 1
 Next
 state(i + 1) = attribKV
 End If
 Next
 ' return either baseState or state, depending on whether or not
 ' any ListItems had attributes
 If (itemHasAttributes) Then
 Return state
 Else
 Return baseState
 End If
End Function


Protected Overrides Sub LoadViewState(ByVal savedState As Object)
 If savedState Is Nothing Then Return
 ' see if savedState is an object or object array
 If Not savedState.GetType.GetElementType() Is Nothing AndAlso savedState.GetType.GetElementType().Equals(GetType(Object)) Then

 ' we have just the base state
 MyBase.LoadViewState(savedState(0))
 'we have an array of items with attributes
 Dim state() As Object = savedState
 MyBase.LoadViewState(state(0)) '/ load the base state
 For i As Integer = 1 To state.Length - 1
 If Not state(i) Is Nothing Then
 ' Load back in the attributes
 Dim attribKV() As Object = state(i)
 For k As Integer = 0 To attribKV.Length - 1 Step +2
 Me.Items(i - 1).Attributes.Add(attribKV(k).ToString(), attribKV(k + 1).ToString())
 Next
 End If
 Next
 Else
 'load it normal
 MyBase.LoadViewState(savedState)
 End If
End Sub
</code></pre>

blocks|key|1743538|text|基于上面的帖子，我已经创建了这个控件的一个c#版本，它具有工作视图状态。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743539|++++++++public+const+string+OptionGroupTag+=+"optgroup";
++++private+const+string+OptionTag+=+"option";
++++protected+override+void+RenderContents(System.Web.UI.HtmlTextWriter+writer)
++++{
++++++++ListItemCollection+items+=+this.Items;
++++++++int+count+=+items.Count;
++++++++string+tag;
++++++++string+optgroupLabel;
++++++++if+(count+>+0)
++++++++{
++++++++++++bool+flag+=+false;
++++++++++++for+(int+i+=+0;+i+<+count;+i%2B%2B)
++++++++++++{
++++++++++++++++tag+=+OptionTag;
++++++++++++++++optgroupLabel+=+null;
++++++++++++++++ListItem+item+=+items[i];
++++++++++++++++if+(item.Enabled)
++++++++++++++++{
++++++++++++++++++++if+(item.Attributes+!=+null+&&+item.Attributes.Count+>+0+&&+item.Attributes[OptionGroupTag]+!=+null)
++++++++++++++++++++{
++++++++++++++++++++++++tag+=+OptionGroupTag;
++++++++++++++++++++++++optgroupLabel+=+item.Attributes[OptionGroupTag];
++++++++++++++++++++}
++++++++++++++++++++writer.WriteBeginTag(tag);
++++++++++++++++++++//+NOTE(cboivin):+Is+optionGroup
++++++++++++++++++++if+(!string.IsNullOrEmpty(optgroupLabel))
++++++++++++++++++++{
++++++++++++++++++++++++writer.WriteAttribute("label",+optgroupLabel);
++++++++++++++++++++}
++++++++++++++++++++else
++++++++++++++++++++{
++++++++++++++++++++++++if+(item.Selected)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++if+(flag)
++++++++++++++++++++++++++++{
++++++++++++++++++++++++++++++++this.VerifyMultiSelect();
++++++++++++++++++++++++++++}
++++++++++++++++++++++++++++flag+=+true;
++++++++++++++++++++++++++++writer.WriteAttribute("selected",+"selected");
++++++++++++++++++++++++}
++++++++++++++++++++++++writer.WriteAttribute("value",+item.Value,+true);
++++++++++++++++++++++++if+(item.Attributes+!=+null+&&+item.Attributes.Count+>+0)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++item.Attributes.Render(writer);
++++++++++++++++++++++++}
++++++++++++++++++++++++if+(this.Page+!=+null)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++this.Page.ClientScript.RegisterForEventValidation(this.UniqueID,+item.Value);
++++++++++++++++++++++++}
++++++++++++++++++++}
++++++++++++++++++++writer.Write('>');
++++++++++++++++++++HttpUtility.HtmlEncode(item.Text,+writer);
++++++++++++++++++++writer.WriteEndTag(tag);
++++++++++++++++++++writer.WriteLine();
++++++++++++++++}
++++++++++++}
++++++++}
++++}

++++++++protected+override+object+SaveViewState()
++++{
++++++++object[]+state+=+new+object[this.Items.Count+%2B+1];
++++++++object+baseState+=+base.SaveViewState();
++++++++state[0]+=+baseState;
++++++++bool+itemHasAttributes+=+false;

++++++++for+(int+i+=+0;+i+<+this.Items.Count;+i%2B%2B)
++++++++{
++++++++++++if+(this.Items[i].Attributes.Count+>+0)
++++++++++++{
++++++++++++++++itemHasAttributes+=+true;
++++++++++++++++object[]+attributes+=+new+object[this.Items[i].Attributes.Count+*+2];
++++++++++++++++int+k+=+0;

++++++++++++++++foreach+(string+key+in+this.Items[i].Attributes.Keys)
++++++++++++++++{
++++++++++++++++++++attributes[k]+=+key;
++++++++++++++++++++k%2B%2B;
++++++++++++++++++++attributes[k]+=+this.Items[i].Attributes[key];
++++++++++++++++++++k%2B%2B;
++++++++++++++++}
++++++++++++++++state[i+%2B+1]+=+attributes;
++++++++++++}
++++++++}

++++++++if+(itemHasAttributes)
++++++++++++return+state;
++++++++return+baseState;
++++}

++++++++protected+override+void+LoadViewState(object+savedState)
++++{
++++++++if+(savedState+==+null)
++++++++++++return;

++++++++if+(!(savedState.GetType().GetElementType()+==+null)+&&
++++++++++++(savedState.GetType().GetElementType().Equals(typeof(object))))
++++++++{
++++++++++++object[]+state+=+(object[])savedState;
++++++++++++base.LoadViewState(state[0]);

++++++++++++for+(int+i+=+1;+i+<+state.Length;+i%2B%2B)
++++++++++++{
++++++++++++++++if+(state[i]+!=+null)
++++++++++++++++{
++++++++++++++++++++object[]+attributes+=+(object[])state[i];
++++++++++++++++++++for+(int+k+=+0;+k+<+attributes.Length;+k+%2B=+2)
++++++++++++++++++++{
++++++++++++++++++++++++this.Items[i+-+1].Attributes.Add
++++++++++++++++++++++++++++(attributes[k].ToString(),+attributes[k+%2B+1].ToString());
++++++++++++++++++++}
++++++++++++++++}
++++++++++++}
++++++++}
++++++++else
++++++++{
++++++++++++base.LoadViewState(savedState);
++++++++}
++++}|code-block|syntax|javascript|1743540|我希望这对一些人有帮助:-)|1743541|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Based on the posts above I've created a c# version of this control with working view state.

<pre><code> public const string OptionGroupTag = "optgroup";
 private const string OptionTag = "option";
 protected override void RenderContents(System.Web.UI.HtmlTextWriter writer)
 {
 ListItemCollection items = this.Items;
 int count = items.Count;
 string tag;
 string optgroupLabel;
 if (count &gt; 0)
 {
 bool flag = false;
 for (int i = 0; i &lt; count; i++)
 {
 tag = OptionTag;
 optgroupLabel = null;
 ListItem item = items[i];
 if (item.Enabled)
 {
 if (item.Attributes != null &amp;&amp; item.Attributes.Count &gt; 0 &amp;&amp; item.Attributes[OptionGroupTag] != null)
 {
 tag = OptionGroupTag;
 optgroupLabel = item.Attributes[OptionGroupTag];
 }
 writer.WriteBeginTag(tag);
 // NOTE(cboivin): Is optionGroup
 if (!string.IsNullOrEmpty(optgroupLabel))
 {
 writer.WriteAttribute("label", optgroupLabel);
 }
 else
 {
 if (item.Selected)
 {
 if (flag)
 {
 this.VerifyMultiSelect();
 }
 flag = true;
 writer.WriteAttribute("selected", "selected");
 }
 writer.WriteAttribute("value", item.Value, true);
 if (item.Attributes != null &amp;&amp; item.Attributes.Count &gt; 0)
 {
 item.Attributes.Render(writer);
 }
 if (this.Page != null)
 {
 this.Page.ClientScript.RegisterForEventValidation(this.UniqueID, item.Value);
 }
 }
 writer.Write('&gt;');
 HttpUtility.HtmlEncode(item.Text, writer);
 writer.WriteEndTag(tag);
 writer.WriteLine();
 }
 }
 }
 }

 protected override object SaveViewState()
 {
 object[] state = new object[this.Items.Count + 1];
 object baseState = base.SaveViewState();
 state[0] = baseState;
 bool itemHasAttributes = false;

 for (int i = 0; i &lt; this.Items.Count; i++)
 {
 if (this.Items[i].Attributes.Count &gt; 0)
 {
 itemHasAttributes = true;
 object[] attributes = new object[this.Items[i].Attributes.Count * 2];
 int k = 0;

 foreach (string key in this.Items[i].Attributes.Keys)
 {
 attributes[k] = key;
 k++;
 attributes[k] = this.Items[i].Attributes[key];
 k++;
 }
 state[i + 1] = attributes;
 }
 }

 if (itemHasAttributes)
 return state;
 return baseState;
 }

 protected override void LoadViewState(object savedState)
 {
 if (savedState == null)
 return;

 if (!(savedState.GetType().GetElementType() == null) &amp;&amp;
 (savedState.GetType().GetElementType().Equals(typeof(object))))
 {
 object[] state = (object[])savedState;
 base.LoadViewState(state[0]);

 for (int i = 1; i &lt; state.Length; i++)
 {
 if (state[i] != null)
 {
 object[] attributes = (object[])state[i];
 for (int k = 0; k &lt; attributes.Length; k += 2)
 {
 this.Items[i - 1].Attributes.Add
 (attributes[k].ToString(), attributes[k + 1].ToString());
 }
 }
 }
 }
 else
 {
 base.LoadViewState(savedState);
 }
 }
</code></pre>

I hope this helps some people :-)

blocks|key|1528578|text|上面的代码将optgroup的结束标记呈现在任何选项之前，因此除了不能正确表示分组的标记之外，选项不会像应有的那样缩进。下面是我对Tom的代码稍加修改的版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528579|++++public+class+ExtendedDropDownList+:+System.Web.UI.WebControls.DropDownList
{
++++public+const+string+OptionGroupTag+=+"optgroup";
++++private+const+string+OptionTag+=+"option";
++++protected+override+void+RenderContents(System.Web.UI.HtmlTextWriter+writer)
++++{
++++++++ListItemCollection+items+=+this.Items;
++++++++int+count+=+items.Count;
++++++++string+tag;
++++++++string+optgroupLabel;
++++++++if+(count+>+0)
++++++++{
++++++++++++bool+flag+=+false;
++++++++++++string+prevOptGroup+=+null;
++++++++++++for+(int+i+=+0;+i+<+count;+i%2B%2B)
++++++++++++{
++++++++++++++++tag+=+OptionTag;
++++++++++++++++optgroupLabel+=+null;
++++++++++++++++ListItem+item+=+items[i];
++++++++++++++++if+(item.Enabled)
++++++++++++++++{
++++++++++++++++++++if+(item.Attributes+!=+null+&&+item.Attributes.Count+>+0+&&+item.Attributes[OptionGroupTag]+!=+null)
++++++++++++++++++++{
++++++++++++++++++++++++optgroupLabel+=+item.Attributes[OptionGroupTag];

++++++++++++++++++++++++if+(prevOptGroup+!=+optgroupLabel)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++if+(prevOptGroup+!=+null)
++++++++++++++++++++++++++++{
++++++++++++++++++++++++++++++++writer.WriteEndTag(OptionGroupTag);
++++++++++++++++++++++++++++}
++++++++++++++++++++++++++++writer.WriteBeginTag(OptionGroupTag);
++++++++++++++++++++++++++++if+(!string.IsNullOrEmpty(optgroupLabel))
++++++++++++++++++++++++++++{
++++++++++++++++++++++++++++++++writer.WriteAttribute("label",+optgroupLabel);
++++++++++++++++++++++++++++}
++++++++++++++++++++++++++++writer.Write('>');
++++++++++++++++++++++++}
++++++++++++++++++++++++item.Attributes.Remove(OptionGroupTag);
++++++++++++++++++++++++prevOptGroup+=+optgroupLabel;
++++++++++++++++++++}
++++++++++++++++++++else
++++++++++++++++++++{
++++++++++++++++++++++++if+(prevOptGroup+!=+null)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++writer.WriteEndTag(OptionGroupTag);
++++++++++++++++++++++++}
++++++++++++++++++++++++prevOptGroup+=+null;
++++++++++++++++++++}

++++++++++++++++++++writer.WriteBeginTag(tag);
++++++++++++++++++++if+(item.Selected)
++++++++++++++++++++{
++++++++++++++++++++++++if+(flag)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++this.VerifyMultiSelect();
++++++++++++++++++++++++}
++++++++++++++++++++++++flag+=+true;
++++++++++++++++++++++++writer.WriteAttribute("selected",+"selected");
++++++++++++++++++++}
++++++++++++++++++++writer.WriteAttribute("value",+item.Value,+true);
++++++++++++++++++++if+(item.Attributes+!=+null+&&+item.Attributes.Count+>+0)
++++++++++++++++++++{
++++++++++++++++++++++++item.Attributes.Render(writer);
++++++++++++++++++++}
++++++++++++++++++++if+(optgroupLabel+!=+null)
++++++++++++++++++++{
++++++++++++++++++++++++item.Attributes.Add(OptionGroupTag,+optgroupLabel);
++++++++++++++++++++}
++++++++++++++++++++if+(this.Page+!=+null)
++++++++++++++++++++{
++++++++++++++++++++++++this.Page.ClientScript.RegisterForEventValidation(this.UniqueID,+item.Value);
++++++++++++++++++++}

++++++++++++++++++++writer.Write('>');
++++++++++++++++++++HttpUtility.HtmlEncode(item.Text,+writer);
++++++++++++++++++++writer.WriteEndTag(tag);
++++++++++++++++++++writer.WriteLine();
++++++++++++++++++++if+(i+==+count+-+1)
++++++++++++++++++++{
++++++++++++++++++++++++if+(prevOptGroup+!=+null)
++++++++++++++++++++++++{
++++++++++++++++++++++++++++writer.WriteEndTag(OptionGroupTag);
++++++++++++++++++++++++}
++++++++++++++++++++}
++++++++++++++++}
++++++++++++}
++++++++}
++++}

++++protected+override+object+SaveViewState()
++++{
++++++++object[]+state+=+new+object[this.Items.Count+%2B+1];
++++++++object+baseState+=+base.SaveViewState();
++++++++state[0]+=+baseState;
++++++++bool+itemHasAttributes+=+false;

++++++++for+(int+i+=+0;+i+<+this.Items.Count;+i%2B%2B)
++++++++{
++++++++++++if+(this.Items[i].Attributes.Count+>+0)
++++++++++++{
++++++++++++++++itemHasAttributes+=+true;
++++++++++++++++object[]+attributes+=+new+object[this.Items[i].Attributes.Count+*+2];
++++++++++++++++int+k+=+0;

++++++++++++++++foreach+(string+key+in+this.Items[i].Attributes.Keys)
++++++++++++++++{
++++++++++++++++++++attributes[k]+=+key;
++++++++++++++++++++k%2B%2B;
++++++++++++++++++++attributes[k]+=+this.Items[i].Attributes[key];
++++++++++++++++++++k%2B%2B;
++++++++++++++++}
++++++++++++++++state[i+%2B+1]+=+attributes;
++++++++++++}
++++++++}

++++++++if+(itemHasAttributes)
++++++++++++return+state;
++++++++return+baseState;
++++}

++++protected+override+void+LoadViewState(object+savedState)
++++{
++++++++if+(savedState+==+null)
++++++++++++return;

++++++++if+(!(savedState.GetType().GetElementType()+==+null)+&&
++++++++++++(savedState.GetType().GetElementType().Equals(typeof(object))))
++++++++{
++++++++++++object[]+state+=+(object[])savedState;
++++++++++++base.LoadViewState(state[0]);

++++++++++++for+(int+i+=+1;+i+<+state.Length;+i%2B%2B)
++++++++++++{
++++++++++++++++if+(state[i]+!=+null)
++++++++++++++++{
++++++++++++++++++++object[]+attributes+=+(object[])state[i];
++++++++++++++++++++for+(int+k+=+0;+k+<+attributes.Length;+k+%2B=+2)
++++++++++++++++++++{
++++++++++++++++++++++++this.Items[i+-+1].Attributes.Add
++++++++++++++++++++++++++++(attributes[k].ToString(),+attributes[k+%2B+1].ToString());
++++++++++++++++++++}
++++++++++++++++}
++++++++++++}
++++++++}
++++++++else
++++++++{
++++++++++++base.LoadViewState(savedState);
++++++++}
++++}
}|code-block|syntax|javascript|1528580|像这样使用它：|1528581|++++++++++++ListItem+item1+=+new+ListItem("option1");
++++++++item1.Attributes.Add("optgroup",+"CatA");
++++++++ListItem+item2+=+new+ListItem("option2");
++++++++item2.Attributes.Add("optgroup",+"CatA");
++++++++ListItem+item3+=+new+ListItem("option3");
++++++++item3.Attributes.Add("optgroup",+"CatB");
++++++++ListItem+item4+=+new+ListItem("option4");
++++++++item4.Attributes.Add("optgroup",+"CatB");
++++++++ListItem+item5+=+new+ListItem("NoOptGroup");

++++++++ddlTest.Items.Add(item1);
++++++++ddlTest.Items.Add(item2);
++++++++ddlTest.Items.Add(item3);
++++++++ddlTest.Items.Add(item4);
++++++++ddlTest.Items.Add(item5);|1528582|下面是生成的标记(缩进以便于查看)：|1528583|+<select+name="ddlTest"+id="Select1">
++++<optgroup+label="CatA">
++++++++<option+selected="selected"+value="option1">option1</option>
++++++++<option+value="option2">option2</option>
++++</optgroup>
++++<optgroup+label="CatB">
++++++++<option+value="option3">option3</option>
++++++++<option+value="option4">option4</option>
++++</optgroup>
++++<option+value="NoOptGroup">NoOptGroup</option>
+</select>|1528584|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

The above code renders the end tag for the optgroup before any of the options, so the options don't get indented like they should in addition to the markup not properly representing the grouping. Here's my slightly modified version of Tom's code:

<pre><code> public class ExtendedDropDownList : System.Web.UI.WebControls.DropDownList
{
 public const string OptionGroupTag = "optgroup";
 private const string OptionTag = "option";
 protected override void RenderContents(System.Web.UI.HtmlTextWriter writer)
 {
 ListItemCollection items = this.Items;
 int count = items.Count;
 string tag;
 string optgroupLabel;
 if (count &gt; 0)
 {
 bool flag = false;
 string prevOptGroup = null;
 for (int i = 0; i &lt; count; i++)
 {
 tag = OptionTag;
 optgroupLabel = null;
 ListItem item = items[i];
 if (item.Enabled)
 {
 if (item.Attributes != null &amp;&amp; item.Attributes.Count &gt; 0 &amp;&amp; item.Attributes[OptionGroupTag] != null)
 {
 optgroupLabel = item.Attributes[OptionGroupTag];

 if (prevOptGroup != optgroupLabel)
 {
 if (prevOptGroup != null)
 {
 writer.WriteEndTag(OptionGroupTag);
 }
 writer.WriteBeginTag(OptionGroupTag);
 if (!string.IsNullOrEmpty(optgroupLabel))
 {
 writer.WriteAttribute("label", optgroupLabel);
 }
 writer.Write('&gt;');
 }
 item.Attributes.Remove(OptionGroupTag);
 prevOptGroup = optgroupLabel;
 }
 else
 {
 if (prevOptGroup != null)
 {
 writer.WriteEndTag(OptionGroupTag);
 }
 prevOptGroup = null;
 }

 writer.WriteBeginTag(tag);
 if (item.Selected)
 {
 if (flag)
 {
 this.VerifyMultiSelect();
 }
 flag = true;
 writer.WriteAttribute("selected", "selected");
 }
 writer.WriteAttribute("value", item.Value, true);
 if (item.Attributes != null &amp;&amp; item.Attributes.Count &gt; 0)
 {
 item.Attributes.Render(writer);
 }
 if (optgroupLabel != null)
 {
 item.Attributes.Add(OptionGroupTag, optgroupLabel);
 }
 if (this.Page != null)
 {
 this.Page.ClientScript.RegisterForEventValidation(this.UniqueID, item.Value);
 }

 writer.Write('&gt;');
 HttpUtility.HtmlEncode(item.Text, writer);
 writer.WriteEndTag(tag);
 writer.WriteLine();
 if (i == count - 1)
 {
 if (prevOptGroup != null)
 {
 writer.WriteEndTag(OptionGroupTag);
 }
 }
 }
 }
 }
 }

 protected override object SaveViewState()
 {
 object[] state = new object[this.Items.Count + 1];
 object baseState = base.SaveViewState();
 state[0] = baseState;
 bool itemHasAttributes = false;

 for (int i = 0; i &lt; this.Items.Count; i++)
 {
 if (this.Items[i].Attributes.Count &gt; 0)
 {
 itemHasAttributes = true;
 object[] attributes = new object[this.Items[i].Attributes.Count * 2];
 int k = 0;

 foreach (string key in this.Items[i].Attributes.Keys)
 {
 attributes[k] = key;
 k++;
 attributes[k] = this.Items[i].Attributes[key];
 k++;
 }
 state[i + 1] = attributes;
 }
 }

 if (itemHasAttributes)
 return state;
 return baseState;
 }

 protected override void LoadViewState(object savedState)
 {
 if (savedState == null)
 return;

 if (!(savedState.GetType().GetElementType() == null) &amp;&amp;
 (savedState.GetType().GetElementType().Equals(typeof(object))))
 {
 object[] state = (object[])savedState;
 base.LoadViewState(state[0]);

 for (int i = 1; i &lt; state.Length; i++)
 {
 if (state[i] != null)
 {
 object[] attributes = (object[])state[i];
 for (int k = 0; k &lt; attributes.Length; k += 2)
 {
 this.Items[i - 1].Attributes.Add
 (attributes[k].ToString(), attributes[k + 1].ToString());
 }
 }
 }
 }
 else
 {
 base.LoadViewState(savedState);
 }
 }
}
</code></pre>

Use it like this:

<pre><code> ListItem item1 = new ListItem("option1");
 item1.Attributes.Add("optgroup", "CatA");
 ListItem item2 = new ListItem("option2");
 item2.Attributes.Add("optgroup", "CatA");
 ListItem item3 = new ListItem("option3");
 item3.Attributes.Add("optgroup", "CatB");
 ListItem item4 = new ListItem("option4");
 item4.Attributes.Add("optgroup", "CatB");
 ListItem item5 = new ListItem("NoOptGroup");

 ddlTest.Items.Add(item1);
 ddlTest.Items.Add(item2);
 ddlTest.Items.Add(item3);
 ddlTest.Items.Add(item4);
 ddlTest.Items.Add(item5);
</code></pre>

and here's the generated markup (indented for ease of viewing):

<pre><code> &lt;select name="ddlTest" id="Select1"&gt;
 &lt;optgroup label="CatA"&gt;
 &lt;option selected="selected" value="option1"&gt;option1&lt;/option&gt;
 &lt;option value="option2"&gt;option2&lt;/option&gt;
 &lt;/optgroup&gt;
 &lt;optgroup label="CatB"&gt;
 &lt;option value="option3"&gt;option3&lt;/option&gt;
 &lt;option value="option4"&gt;option4&lt;/option&gt;
 &lt;/optgroup&gt;
 &lt;option value="NoOptGroup"&gt;NoOptGroup&lt;/option&gt;
 &lt;/select&gt;
</code></pre>

blocks|key|1743653|text|++++//+How+to+use:
++++//+1.+Create+items+in+a+select+element+or+asp:DropDownList+control
++++//+2.+Set+value+of+an+option+or+ListItem+to+"_group_",+those+will+be+converted+to+optgroups
++++//+3.+On+page+onload+call+createOptGroups(domElement),+for+example+like+this:
++++//++++-+var+lst+=+document.getElementById('lst');
++++//++++-+createOptGroups(lst,+"_group_");
++++//+4.+You+can+change+groupMarkerValue+to+anything,+I+used+"_group_"
++++function+createOptGroups(lst,+groupMarkerValue)+{
++++++++//+Get+an+array+containing+the+options
++++++++var+childNodes+=+[];
++++++++for+(var+i+=+0;+i+<+lst.options.length;+i%2B%2B)
++++++++++++childNodes.push(lst.options[i]);

++++++++//+Get+the+selected+element+so+we+can+preserve+selection
++++++++var+selectedIndex+=+lst.selectedIndex;
++++++++var+selectedChild+=+childNodes[selectedIndex];
++++++++var+selectedValue+=+selectedChild.value;

++++++++//+Remove+all+elements
++++++++while+(lst.hasChildNodes())
++++++++++++lst.removeChild(lst.childNodes[0]);

++++++++//+Go+through+the+array+of+options+and+convert+some+into+groups
++++++++var+group+=+null;
++++++++for+(var+i+=+0;+i+<+childNodes.length;+i%2B%2B)+{
++++++++++++var+node+=+childNodes[i];
++++++++++++if+(node.value+==+groupMarkerValue)+{
++++++++++++++++group+=+document.createElement("optgroup");
++++++++++++++++group.label+=+node.text;
++++++++++++++++group.value+=+groupMarkerValue;
++++++++++++++++lst.appendChild(group);
++++++++++++++++continue;
++++++++++++}

++++++++++++//+Add+to+group+or+directly+under+list
++++++++++++(group+==+null+?+lst+:+group).appendChild(node);
++++++++}

++++++++//+Preserve+selected,+no+support+for+multi-selection+here,+sorry
++++++++selectedChild.selected+=+true;
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1743654|在Chrome16、Firefox9和IE8上进行了测试。|unstyled|1743655|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code> // How to use:
 // 1. Create items in a select element or asp:DropDownList control
 // 2. Set value of an option or ListItem to "_group_", those will be converted to optgroups
 // 3. On page onload call createOptGroups(domElement), for example like this:
 // - var lst = document.getElementById('lst');
 // - createOptGroups(lst, "_group_");
 // 4. You can change groupMarkerValue to anything, I used "_group_"
 function createOptGroups(lst, groupMarkerValue) {
 // Get an array containing the options
 var childNodes = [];
 for (var i = 0; i &lt; lst.options.length; i++)
 childNodes.push(lst.options[i]);

 // Get the selected element so we can preserve selection
 var selectedIndex = lst.selectedIndex;
 var selectedChild = childNodes[selectedIndex];
 var selectedValue = selectedChild.value;

 // Remove all elements
 while (lst.hasChildNodes())
 lst.removeChild(lst.childNodes[0]);

 // Go through the array of options and convert some into groups
 var group = null;
 for (var i = 0; i &lt; childNodes.length; i++) {
 var node = childNodes[i];
 if (node.value == groupMarkerValue) {
 group = document.createElement("optgroup");
 group.label = node.text;
 group.value = groupMarkerValue;
 lst.appendChild(group);
 continue;
 }

 // Add to group or directly under list
 (group == null ? lst : group).appendChild(node);
 }

 // Preserve selected, no support for multi-selection here, sorry
 selectedChild.selected = true;
 }
</code></pre>

Tested on Chrome 16, Firefox 9 and IE8.

Can anyone recommend a dropdownlist control for asp.net (3.5) that can render option groups? Thanks

Dropdownlist control with <optgroup>s for asp.net (webforms)?

有没有人能推荐一个可以呈现选项组的asp.net (3.5)的dropdownlist控件？谢谢

问asp.net的<optgroup>s下拉列表控件(webforms)？
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